Surface acidity of water probed by free energy calculation for trimethylamine protonation

Yusuke Tabe; Nobuaki Kikkawa; Hideaki Takahashi; Akihiro Morita

doi:10.1021/jp4078882

Surface acidity of water probed by free energy calculation for trimethylamine protonation

Yusuke Tabe, Nobuaki Kikkawa, Hideaki Takahashi, Akihiro Morita

SCI - Chemistry

Research output: Contribution to journal › Article › peer-review

12 Citations (Scopus)

Abstract

Surface acidity/basicity of water has been elusive, due to contradicting observations from various aspects. One effective definition has been proposed by investigating the protonation equilibrium (pK_a) of the indicator species at the water surface. We calculated the pK_a of trimethylamine at the surface by using quantum mechanics/molecular mechanics (QM/MM) and thermodynamic integration calculations and elucidated the observed pK _a shift at the surface. It was revealed that the observed pK _a shift reflects specific properties of the indicator species, particularly relative solvation free energy at the surface. The pK_a shift appears within ∼5 Å thickness. One has to properly take account of the specific indicators toward deriving a general picture of surface acidity/basicity from protonation reactions.

Original language	English
Pages (from-to)	977-988
Number of pages	12
Journal	Journal of Physical Chemistry C
Volume	118
Issue number	2
DOIs	https://doi.org/10.1021/jp4078882
Publication status	Published - 2014 Jan 16

ASJC Scopus subject areas

Electronic, Optical and Magnetic Materials
Energy(all)
Physical and Theoretical Chemistry
Surfaces, Coatings and Films

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title = "Surface acidity of water probed by free energy calculation for trimethylamine protonation",

abstract = "Surface acidity/basicity of water has been elusive, due to contradicting observations from various aspects. One effective definition has been proposed by investigating the protonation equilibrium (pKa) of the indicator species at the water surface. We calculated the pKa of trimethylamine at the surface by using quantum mechanics/molecular mechanics (QM/MM) and thermodynamic integration calculations and elucidated the observed pK a shift at the surface. It was revealed that the observed pK a shift reflects specific properties of the indicator species, particularly relative solvation free energy at the surface. The pKa shift appears within ∼5 {\AA} thickness. One has to properly take account of the specific indicators toward deriving a general picture of surface acidity/basicity from protonation reactions.",

author = "Yusuke Tabe and Nobuaki Kikkawa and Hideaki Takahashi and Akihiro Morita",

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T1 - Surface acidity of water probed by free energy calculation for trimethylamine protonation

AU - Tabe, Yusuke

AU - Kikkawa, Nobuaki

AU - Takahashi, Hideaki

AU - Morita, Akihiro

PY - 2014/1/16

Y1 - 2014/1/16

N2 - Surface acidity/basicity of water has been elusive, due to contradicting observations from various aspects. One effective definition has been proposed by investigating the protonation equilibrium (pKa) of the indicator species at the water surface. We calculated the pKa of trimethylamine at the surface by using quantum mechanics/molecular mechanics (QM/MM) and thermodynamic integration calculations and elucidated the observed pK a shift at the surface. It was revealed that the observed pK a shift reflects specific properties of the indicator species, particularly relative solvation free energy at the surface. The pKa shift appears within ∼5 Å thickness. One has to properly take account of the specific indicators toward deriving a general picture of surface acidity/basicity from protonation reactions.

AB - Surface acidity/basicity of water has been elusive, due to contradicting observations from various aspects. One effective definition has been proposed by investigating the protonation equilibrium (pKa) of the indicator species at the water surface. We calculated the pKa of trimethylamine at the surface by using quantum mechanics/molecular mechanics (QM/MM) and thermodynamic integration calculations and elucidated the observed pK a shift at the surface. It was revealed that the observed pK a shift reflects specific properties of the indicator species, particularly relative solvation free energy at the surface. The pKa shift appears within ∼5 Å thickness. One has to properly take account of the specific indicators toward deriving a general picture of surface acidity/basicity from protonation reactions.

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Surface acidity of water probed by free energy calculation for trimethylamine protonation

Abstract

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